Quantifies CO2 offset in vegetation from nuclear power plants, indicating local effects on carbon analysis.
Top-down quantification of fossil fuel-derived CO 2 (CO 2ff ) using radiocarbon ( 14 C) relies on the Suess effect, whereby 14 C-free fossil emissions dilute atmospheric 14 CO 2 . However, 14 C releases from nuclear power plants (NPPs) increase the level of ambient 14 CO 2, offsetting fossil dilution and biasing CO 2ff low. Pressurized water reactors (PWRs), dominant in China, emit most 14 C as 14 CH 4, but the smaller 14 CO 2 fraction may still affect nearby air. We investigated the influence of PWR-derived 14 CO 2 from the Daya Bay and Lingao NPPs (Shenzhen, China) using grass samples collected in January 2025, representing 2024 growing-season carbon, together with a previously published 2022 vegetation Δ 14 C data set for comparison and joint spatial analysis. The results show detectable 14 CO 2 enrichment, with positive Δ 14 C values up to +3.2‰, confined to the northern near field (<5 km downwind). Outside this zone, Δ 14 C remained negative overall (−13.1‰ to −42.1‰), with no consistent 14 CO 2 enrichment at more distant sites or south of the NPPs. A first-order CO 2ff -equivalent calculation indicates that this enrichment has an offsetting capacity of 8.3–8.8 ppm of CO 2ff, exceeding the median apparent CO 2ff signal at sites beyond ∼5 km. These findings demonstrate that PWR-derived 14 CO 2 can cause localized, directional interference in Δ 14 C-based CO 2ff reconstructions and highlight the need to integrate nuclear 14 C footprints into top-down CO 2ff frameworks.
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